1. Field of the Invention
The present invention relates to a machining centre for processing a workpiece with a tool supported on a spindle and rotated, and a contouring process using the machining centre, as well as structures of various sections of the machining centre.
2. Description of the Related Art
There is a machine tool conventionally known from Japanese Patent Application Laid-Open No. 61-188011, which is used when a plurality of crankshaft supporting holes provided in a cylinder block are made simultaneously by boring, or when a plurality of cam shaft supporting holes provided in a cylinder head are made simultaneously by boring. This machine tool is designed, so that inner peripheral surfaces of a plurality of bottom holes in a workpiece are bored by a plurality of cutting blades provided at predetermined distances on a shaft-shaped tool body of a tool by inserting the cutting blades into the bottom holes, while rotating the tool.
In the above known machine tool, the inside diameter of the hole being made by one type of tool is limited to the one type. For this reason, there is a problem that if an attempt is made to make a plurality of types of holes having different inside diameters, a large number of tools are required, resulting in an increase in cost. Another problem is that if the cutting blades of the tool become worn, the inside diameter of the hole processed is smaller than a desired size, and for this reason, the life of the tool is limited significantly. Moreover, when a tail support is supported at an upper end of a tail-support supporting member rising from the bed, in a case where the level of a spindle from a bed has been raised due to the supporting of the spindle on the column rising from the bed, the rigidity of the tail-support supporting member itself is insufficient and hence, the tail support may be moved by a reaction force to the processing, whereby the free end of the tool cannot be supported with good accuracy in some cases.
There is also a tool changer known from, for example, Japanese Patent Application Laid-Open No. 8-52641, which is designed, so that a tool can be grasped by each of a plurality of chucks mounted at predetermined distances on a circulating endless chain, and the delivery of the tool is conducted between any of the chucks and a spindle of a machine tool.
When the tool is grasped by the chuck mounted on the endless chain of the tool changer and driven in a circulatory movement, it is necessary to lock the chuck into a non-openable state in order to prevent the dropping of the tool. In addition, when the delivery of the tool is conducted between the chuck and the spindle, it is necessary to unlock the chuck. For this purpose, if a special actuator is provided in a tool delivery position to lock and unlock the chuck, the following problem arises: the number of parts is increased to cause an increase in cost.
In a Curvic coupling device (Curvic: trademark) for indexing a turntable rotatably carried on a base through a bearing and positioned radially, to a predetermined rotational angle to position the turntable, when a coupling member fixed to the base and a coupling member fixed to the turntable are integrally coupled to each other by a coupling member mounted on the base for advancing and retracting movement, the turntable is aligned with respect to the base by an aligning effect applied to between the coupling members each having radial teeth. When the turntable has been positioned radially with respect to the base by a bearing at this time, there is a possibility that the aligning effect possessed by the bearing itself and the aligning effect of the Curvic coupling, interfere with each other due to small processing errors of the bearing and the Curvic coupling. This causes a problem in the aligning effect of the Curvic coupling, resulting not only in a reduction in accuracy of indexing of the turntable, but also in a reduction in durability of the bearing and the Curvic coupling.
Therefore, there is a system proposed in Japanese Patent Application Laid-Open No. 8-52641, which is designed, so that when a turntable is to be indexed by rotation thereof in a state in which the coupling of the Curvic coupling has been released, the turntable is moved axially and supported on a bearing, and when indexing is finished to couple the Curvic coupling, the turntable is moved in an opposite direction to produce a clearance between the turntable and the bearing, so that even if the turntable is moved radially by the aligning effect of the Curvic coupling, no load is applied to the bearing.
However, the above known system suffers from a problem that the structure for axially moving the turntable to support it on the bearing and to produce the clearance is complicated, resulting in increases in number of parts and in cost.
A pallet changer is known from Japanese Utility Model Application Laid-Open No. 63-140330, which includes a transporting-in means and a transporting-out means provided vertically in two stages and capable of supporting a pallet for the placement of a workpiece, so that the following operations are carried out automatically: an operation of transporting the pallet from the transporting-in means to a lifting/lowering frame of a pressing-in device, and an operation of transporting the pallet from the lifting/lowering frame to the transporting-out means.
This pallet changer is designed, so that a cylinder is connected to the pallet by bringing an arm piece turned by a drive source into engagement with an engage pin of the pallet, in order to move the pallet by urging or pulling it by the cylinder to conduct the delivery of the pallet between the transporting in means as well as the transporting-out means and the lifting/lowering frame of the pressing-in device.
However, the above known pallet changer suffers from a problem that to connect or disconnect the cylinder for moving the pallet, to or from the pallet, a special drive source for turning the arm piece is required, resulting in an increase in number of parts and in a complicated structure.